This invention involves a use for rubber scrap from discarded automobile tires.
It has been estimated that roughly 3 billion discarded tires from automobiles and trucks litter the American landscape, and 200 million more are discarded every year. Although some discarded tires are dumped offshore to create fishing reefs, that method of disposal is impractical for tires located long distances from coastlines. Most discarded tires sit in open dumps, where they collect rainwater and serve as breeding grounds for mosquitos, rats, and other pests. More information on various problems relating to the disposal or recycling of discarded tires is contained in the introductory section of U.S. Pat. No. 4,726,530 (Miller and Priscu 1988).
Various machines have been developed to cut, grind, or shred discarded tires into fragments. Such machines are disclosed in, e.g., U.S. Pat. Nos. 3,561,308 (Ehrlich 1971), 4,405,090 (Wakeem 1983), 4,422,581 (Chryst 1983), and 4,757,949 (Horton 1988).
More elaborate systems that can remove strands or pieces of steel, fiberglass, polyester, nylon, or other materials used in the reinforcing belts, so that the remaining purified rubber fragments can be chemically processed, are described in various other patents such as U.S. Pat. Nos. 4,726,530 (Miller and Priscu 1988) and 4,813,614 (Moore and Aten 1989). However, such additional processing tends to be relatively expensive.
A number of proposals have been made for using rubber from recycled tires in various shaped forms. These uses involve mixing the rubber an adhesive such as asphalt (e.g., U.S. Pat. No. 2,977,864, Pullar 1961), a sulfur compound (see U.S. Pat. No. 4,244,B41, Frankland 1981), or a thermosetting resin (e.g., U.S. Pat. No. 3,344,094, deGaugue 1967) to create a viscous, sticky mixture which is cured or dried to create a dry solid article. Some of these of items of prior art also state that fibers or additional components are necessary to provide adequate strength for the intended uses. In some cases, the adhesive mixture is spread in a relatively thin layer across a flat surface and allowed to dry, thereby forming a rubberized and somewhat cushioned surface which adheres tightly to the surface it is placed upon (see, e.g., U.S. Pat. No. 3,801,421, Allen et al 1974). In other cases, the mixture is placed in a mold and cured to create a desired shape.
A number of patents state that items made from recycled tire fragments can be used as railroad tie pads. Railroad tie pads are not the same as railroad ties. A railroad tie (also called a cross-tie) is a large piece of wood, usually about 7 by 9 inches (about 18 by 23 cm) thick and about 8 feet (2.5 meters) long; each railroad tie rests beneath both rails on a railroad track. By contrast, a tie pad is a much smaller flat piece which is almost square and which rests beneath a single steel rail, on top of a single wooden tie; a tie pad has a hole in its center, through which a railroad spike passes. The tie pad helps dampen and suppress motion by the spike, which otherwise would vibrate and move excessively when a train is passing across the rail. In this manner, tie pads help prolong the useful lives of the railroad ties. By using rubber tie pads beneath the steel rails, it is possible to provide a small but significant degree of cushioning for both the train and the track. U.S. patents which describe the use of tie pads made of recycled tire particles include U.S. Pat. Nos. 2,686,009 (Crowe 1954); 2,713,013 (Spokes 1955); 2,880,127 (Spokes 1959); 2,886,248 (Laudig 1959); 2,892,592 (Greene and Thurston 1959); and 3,081,035 (Meyer 1963).
Another item of prior art relating to molded mixtures containing rubber particles from recycled tires is British patent GB 1 586 882 (assigned to the Winson Luxemburg company; published on Mar. 25, 1981). This British patent requires particular attention since it mentions, in passing, the possibility of using the molded items as railroad ties, which is the subject matter of the current disclosure. GB patent 1,586,882 states that a "particulate synthetic thermoplastic resin material" should be used as the adhesive, but it provides no additional or specific information on such adhesives. It also provides no information on the molding or curing process, except to say that the initial mixture should contain both "molten" tire particles mixed with adhesive, and non-molten tire particles. It also states that: (1) all metal particles should be removed from the rubber, which will greatly increase the cost of obtaining such particles from steel-belted tires; (b) the rubber should be mixed with 20 to 50 percent plastic or fiberglass, preferably obtained from waste material; and, (c) if 50% of the material is plastic rather than rubber, then the material is relatively non-porous, but if only 20% plastic is used, the resulting mix become highly porous. It asserts that the resulting molded items can be used as flower pots, minnow pails, garbage cans, and buckets. It also asserts that such articles can also be used as railroad ties, but it contains no information to indicate that the necessary strengths or durabilities for such use can be achieved, and it makes the unsupported assertion that such items would be "obviously less expensive than currently used counterparts . . . "
In point of fact, the work done by the Applicant indicates that the cost of each tie made of recycled rubber particles will be substantially higher than the cost of wooden railroad ties. The typical cost of a wooden railroad tie, including the cost of treating it with creosote to prevent fungal or insect attack or other deterioration, is about 20 to 30 dollars, which does not include installation cost. By comparison, the cost of a railroad tie made of recycled tire particles, using a type of adhesive which is suitable for use in railroad ties and in sufficient quantity of adhesive to ensure complete adhesion to eliminate the danger of cracking in areas that have not be adequately contacted by adhesive, is currently in excess of $50 per tie.
Nevertheless, the Applicant has discovered that in some situations, railroad ties made of recycled rubber are sufficiently strong and durable to render them economically feasible and even preferable in some environments where wooden ties have short lifespans. This is especially true in regions with frequent snow or rain that are subject to frequent cycling above and below the freezing point of water; the frequency of cycling above and below freezing is more important than average temperatures, since each time the temperature drops below freezing, any rainfall or melted snow which has coated or seeped into the tie will freeze, and the expansion of the ice as it freezes forces apart the fibers in the wood, causing it to crack and split. In some environments, wooden ties show substantial signs of wear within two or three years, and must be replaced often to ensure adequate margins of safety for the trains passing over them. Replacement is a very expensive process; the cost of labor, new spikes, new tie pads, lost travel time on the rails, and other related expenses for removing cracked ties and installing new ties beneath a railroad usually amount to substantially more than the cost of the ties.
Accordingly, despite the availability of machinery for cutting, grinding, or shredding tires into fragments of any desired size, and despite the existence of numerous patents and other publications which suggest various uses for rubber fragments from recycled tires, the fact remains that millions of discarded tires continue to be added every year to open dumps, where they become eyesores and breeding grounds for pests. Not enough practical and economic uses have been undertaken to actually use and recycle discarded tires.
Therefore, one object of the subject invention is to disclose a method of using rubber fragments obtained from discarded tires, in railroad ties which can be placed beneath railroads in an economically feasible and competitive manner.
Another object of the invention is to provide a use for discarded tires which can utilize fragments of rubber without requiring expensive processing to remove strands of steel, fiberglass, polyester, nylon, or other reinforcing material from the rubber.
A third object of the subject invention is to provide a method of recycling discarded tires into products that will substitute for lumber in railroad ties, thereby reducing the number of trees that must be cut down in order to provide products that people need.